This invention relates to apparatus for treating waste water.
Generally, treatment of waste water containing soluble organic matter is done by decomposing the organic matter through the proliferation of microorganisms. Such treatment is referred to as biological treatment, and there are two basic methods of treatment, one known as activated sludge process and the other as tricking filtration process.
The activated sludge process is effective for use at such facilities as sewage disposal plants where mass treatment operation is required, but it involves maintenance and control difficulty. The trickling filtration provides ease of maintenance and control, but on the other hand it has a disadvantage in that the rate of BOD removal it affords is relatively low.
A known improved arrangement for biological treatment of waste water is to utilize rotating biological contactors (typically in the form of discs). Known as rotating biological contactor process, it provides a combination of advantages of both activated sludge process and trickling filtration process, such as ease of maintenance and control, high treatment efficiency, and smaller plant scale required. Hence, the rotating biological contactor process has been in wide use and thus far a number of improvements on it have been proposed.
However, with various rotating contactor systems so far developed there has still remained room for improvement in respect of their performance.
Accordingly, it is the primary object of this invention to provide a wastewater treatment system employing a rotating drum which provides a larger filtration area, and hence higher treatment efficiency, than any known treatment arrangement utilizing rotating biological contactors, typically discs. In the rotating drum system according to the invention, the drum incorporates a multiplicity of biological contactors of a specific configuration designed to provide a larger filtration area than discs. More concretely, a wastewater treatment apparatus in accordance with the invention comprises a wastewater tank, a water pervious drum rotatably horizontally fixed mounted in the tank and submerged about one half of its diameter in wastewater in the tank, and a multiplicity of biological contactors packed in the drum, wherein the drum, at least its peripheral wall portion, is constructed of porous plate or woven metal wire so as to be water pervious and the biological contactors are of hollow structure, each having at least two small openings, and are compactly and securely packed in the drum so as to be prevented from movement therein.
In accordance with the invention, the biological contactors packed in the drum are of thin-walled hollow structure. This provides each contactor with a relatively larger surface area of contact with wastewater and thus facilitates wastewater purification. It provides another advantage that the contactors are light in weight, which fact means reduced power requirement for operation. Further, in the wastewater treatment arrangement of the invention, the biological contactors of hollow structure are each provided with at least two small openings and are compactly and securely packed in the drum so as to be prevented from movement therein. This assures that as the drum rotates, wastewater and air go in and out of the hollow portion of the contactors, resulting in effective contact between wastewater and air so that the activity of aerobic microorganisms is stimulated. The fact that the biological contactors are immovable packed in the drum is also advantageous in that it prevents the growth accumelated on the contactor surface from being split therefrom during the rotation of the drum.
A further advantage of the wastewater treatment apparatus of the invention resides in the fact that since the biological contactors packed in the drum are hollow, it is possible to provide a subsidiary biological contactor of a suitable configuration in the interior of each contactor to obtain increased growth accumulation surface and increased area of contact of air and wastewater.
Other feature, objects and advantages of the invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawings.